HELIOS-3E, nicknamed 3E, was an assassin droid who worked for Cad Bane.
HELIOS-3E had light blue markings that were arranged in a striped pattern throughout his entire body. He could be seen, almost all of the time, carrying a standard Bounty Hunter blaster rifle. 3E also had built in optical devices, including a red laser sight and a flashlight.
When Cad Bane received instructions to find plans for the Senate Building, HELIOS-3E captured C-3PO after TODO-360 successfully lured R2-D2 away into a local Droid Spa. 3E brought C-3PO to Cad Bane, who searched through his memory for the much needed plans. Realizing that C-3PO did not hold the plans, HELIOS-3E was ordered to return to Coruscant to search for R2-D2 with TODO-360. The search did not take long for R2-D2 gave himself up to the assassin droid. Once the plans were successfully extracted from R2-D2s memory, 3E returned to Coruscant once more to dump the astromech droid back into the streets.
HELIOS 3E was a part of Cad Bane's party, alongside Aura Sing, Shahan Alama, Robonino, HELIOS-3D, 2 Commando Droids and the Unidentified Assassin Droid. After dispatching the senate commandos, 3E followed Cad Bane down the corridors of the building.
When navigating through the corridors, HELIOS-3E and the unidentified Assassin Droid spotted a lone senate commando, guarding the control room. Ignoring the senate commando's demands, both droids shot him through the chest and breached the door. Eliminating witnesses, the two assassin droids destroyed the four droid crewers working in the control room. Once the group captured the senators, HELIOS-3E stood watch over them until Ziro the Hutt was successfully recaptured.